Formation of carbon structures (e.g., carbon nanotubes, C60 fullerenes, diamond, etc.) can be accomplished in several ways. For example, C60 molecules have been reportedly formed when carbon material is vaporized during application of a substantial amount of heat, such as by application of a flame or an electrical arc.
Single wall carbon nanotubes (SWCNTs) can also be formed by heating a carbon source, such as by laser ablation of a graphite target mixed with a metal catalyst. SWCNTs formation, unlike fullerene formation, can require a catalytic surface, such as a seeded substrate or a small amount of a metal catalyst (e.g., approximately one atomic percent Ni and Co), to provide a location for the SWCNTs to synthesize and grow.
Multiwall carbon nanotubes (MWCNTs) have also been reportedly formed by a chemical vapor deposition (CVD) technique using a vaporized catalyst to deposit MWCNTs on a substrate. More recently, techniques have been developed that reportedly grow nanotubes without catalytic surfaces.
Conventional techniques for growing carbon structures, however, are often difficult to control, since different structures of carbon are formed simultaneously, thereby making it difficult to preferentially synthesize a given structure of carbon without “contamination” by other carbon structures (e.g., by formation and collection of graphite particles/molecules during synthesis of SWCNTs).
Problems encountered while controlling the formation and growth of carbon structures, such as nanotubes and fullerenes can prevent the preferential growth of a carbon structure. For example, if carbon structures located on complex or temperature-sensitive substrates are desired, the heating processes can involve placing the entire substrate in a furnace and exposing it to high temperatures for extended periods of time, for example, 600 to 800 degrees Celsius for MWCNTs and 1,200 degrees Celsius for SWCNTs. Such temperature control, however, can be difficult to accurately generate and control.
As devices that incorporate carbon structures shrink, and their manufacture become more sensitive to environmental processing conditions, more flexible fabrication alternatives are needed, including methods that prevent damage during high temperature bulk heating treatments.